RFID components are becoming more and more important. The advantage of RFID components in contrast to the still common bar codes is that they can be read out electronically without direct visual contact and can be connected to more and more complex modules in an increasingly extremely cost-effective manner. Thus for example the first RFID components were simple transponders which delivered a response signal to an incoming signal. Currently development is proceeding in the direction of RFID components which can be operated without a power supply only by the induction of the electromagnetic radiation of a high frequency signal even together with other functional modules. Mainly memory modules which can be programmed and read out should be mentioned here. Modern RFID components have a coil, preferably a flat coil, a rectifier for converting the AC signal into DC, as well as the aforementioned functional modules.
In the early years the RFID technology was already being used in industry to mark goods in a production chain. A semifinished product received an RFID “label” and could be tracked, registered and monitored up to final installation within a factory. Furthermore RFID technology was also introduced into retail chains in which goods were protected against theft by RFID. Due to increasing miniaturization these components are not only being provided with more functions, but also are becoming increasingly smaller and at the same time cheaper.
One of the main problems is the “coding” of the so-called code reflectors (resonators). Each RFID component has its own “number” (coding) which can be read out. The number is not present as software in a memory which must be read out, but is physically coded in a code reflector. The incoming electromagnetic “read wave” in a (flat) coil induces a current which feeds the RFID circuit. The resonator “returns” as the response signal a coded analog and/or digital signal which is emitted via an antenna. The resonators, in primitive terms, consist of line patterns. By providing line patterns at certain locations the resonant frequencies can be set. The problem is that several RFID chips or resonators are produced on one wafer in order to be able to economically produce a plurality of resonators. Of course each of the RFID chips must have its own “identification”, therefore its own and mainly unique code. Of course a mask could be produced which justifies this circumstance by there being simply a corresponding pattern in the mask at each chip position. However the cost of preparing one mask per wafer is disproportionate. Since to date there has been no possibility of producing “dynamically variable masks”, the production process of the resonators must take place separately from the other structures of the chip.
Until today, to produce resonators lithographic methods have been used in which the line patterns are produced individually. Technical problems are posed by the resolution which constitutes a limiting factor due to the ratio of the wavelength to the aperture. The smaller the patterns, the smaller the wavelengths must also be, and the more complicated the lithographic systems must be; this leads to a corresponding cost explosion.